Homing pigeons (Columba livia) can find their way home with ease.
Scientists have debated how pigeons accomplish this feat. Some
researchers have suggested that pigeons smell their way back home. New
research shows that pigeons can detect magnetic fields that may aid their
travels.

Dr. Cordula Mora and her colleagues at the University of Auckland (New
Zealand) taught pigeons to detect the presence or absence of a magnetic
field. The researchers trained to pigeons to walk to one end of a wooden
tunnel when a magnetic field was turned on and to walk to the opposite end
of the tunnel when the magnetic field was turned off. If the birds walked
to the correct side of the tunnel, they received a food reward.

After the pigeons were trained successfully, the researchers
performed three experiments:

Small magnets were attached to the beaks of the birds. Results: The pigeons could not detect when the magnetic
field was on or off.Conclusion: Pigeons use their magnetic sense to
navigate.

The olfactory cavity was anesthetized.Results: The pigeons could not detect
when the magnetic field was on or off.Conclusion The location of the receptors for the
magnetic sense is in the beak, not the eye.

The trigeminal nerve or the olfactory nerve was cut.Results: When the olfactory nerve was cut, the birds
could still detect magnetic fields.
When the trigeminal nerve was cut, the birds could not
detect magnetic fields.Conclusion: The olfactory nerve, which carries
information about smell, is not necessary for the detection of magnetic
fields. The trigeminal nerve is required for the detection of
magnetic fields.

These results are in line with the theory that bird beaks contain small
magnetic particles called magnetite. Using magnetite, the birds
are able to sense the Earth's magnetic fields that provide information
about location. Turtles and rainbow trout may
use similar magnetic detection systems.